1. Field of the Invention
The present invention relates to sealed components, in particular carrying RF coils and gradient coils for MRI scanners, wherein actuators for active noise control are employed.
2. Description of the Prior Art
Gradient coils in MRI scanners generate magnetic fields that are variable in time and in amplitude. They are operated inside a static basic magnetic field, i.e., in a basic field magnet. Here, dynamic Lorentz forces act on the gradient coil conductors, exciting vibrations in the structure thereof. This results in the production of significant noise during the operation of the scanner.
In order to actively reduce the production of noise, or the intensity of vibration, by a gradient coil, it has been proposed to install actuators (e.g., piezoceramics, magnetostrictive actuators, or the like) at suitable eigenmode-specific locations that during operation generate a counterforce to the Lorentz force of the gradient coil. In this way, in theory a 30 dB reduction in the vibrational amplitudes is quite realistic.
Heretofore, a practical realization of this measure has not occurred, probably due to the difficult technical problem of creating suitable fastening points for the actuators, which enable a transmission of force onto the gradient structure of, typically, around 10 kN per actuator. In each case, the fastening points must be situated inside the resin matrix of the vacuum-sealed coil, so that the points of application of the actuators for the production of a counterforce to the Lorentz force of the gradient coil also are situated at the points where the vibrations that are to be reduced occur.